Remove private Keras imports.

PiperOrigin-RevId: 565502039

Author: fchollet

tensorflow_model_optimization/python/core/sparsity/keras/prune_registry.py

@@ -19,10 +19,16 @@
 from tensorflow_model_optimization.python.core.sparsity.keras import prunable_layer
 
 try:
-  from keras.engine import base_layer  # pylint: disable=g-import-not-at-top
+  # OSS case.
+  import keras  # pylint: disable=g-import-not-at-top
+  if hasattr(keras, 'src'):
+    # Path as seen in pip packages as of TF/Keras 2.13.
+    from keras.src.engine import base_layer  # pylint: disable=g-import-not-at-top,g-importing-member
+  else:
+    from keras.engine import base_layer  # pylint: disable=g-import-not-at-top,g-importing-member
 except ImportError:
-  # Path as seen in pip packages as of TF/Keras 2.13.
-  from keras.src.engine import base_layer  # pylint: disable=g-import-not-at-top
+  # Internal case.
+  base_layer = tf._keras_internal.engine.base_layer  # pylint: disable=protected-access
 
 # TODO(b/139939526): move to public API.